/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.tomcat.util.http.fileupload.util;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * An input stream, which limits its data size. This stream is
 * used, if the content length is unknown.
 */
public abstract class LimitedInputStream extends FilterInputStream implements Closeable {

	/**
	 * The maximum size of an item, in bytes.
	 */
	private final long sizeMax;

	/**
	 * The current number of bytes.
	 */
	private long count;

	/**
	 * Whether this stream is already closed.
	 */
	private boolean closed;

	/**
	 * Creates a new instance.
	 *
	 * @param inputStream The input stream, which shall be limited.
	 * @param pSizeMax    The limit; no more than this number of bytes
	 *                    shall be returned by the source stream.
	 */
	public LimitedInputStream(InputStream inputStream, long pSizeMax) {
		super(inputStream);
		sizeMax = pSizeMax;
	}

	/**
	 * Called to indicate, that the input streams limit has
	 * been exceeded.
	 *
	 * @param pSizeMax The input streams limit, in bytes.
	 * @param pCount   The actual number of bytes.
	 * @throws IOException The called method is expected
	 *                     to raise an IOException.
	 */
	protected abstract void raiseError(long pSizeMax, long pCount)
			throws IOException;

	/**
	 * Called to check, whether the input streams
	 * limit is reached.
	 *
	 * @throws IOException The given limit is exceeded.
	 */
	private void checkLimit() throws IOException {
		if (count > sizeMax) {
			raiseError(sizeMax, count);
		}
	}

	/**
	 * Reads the next byte of data from this input stream. The value
	 * byte is returned as an <code>int</code> in the range
	 * <code>0</code> to <code>255</code>. If no byte is available
	 * because the end of the stream has been reached, the value
	 * <code>-1</code> is returned. This method blocks until input data
	 * is available, the end of the stream is detected, or an exception
	 * is thrown.
	 * <p>
	 * This method
	 * simply performs <code>in.read()</code> and returns the result.
	 *
	 * @return the next byte of data, or <code>-1</code> if the end of the
	 * stream is reached.
	 * @throws IOException if an I/O error occurs.
	 * @see java.io.FilterInputStream#in
	 */
	@Override
	public int read() throws IOException {
		int res = super.read();
		if (res != -1) {
			count++;
			checkLimit();
		}
		return res;
	}

	/**
	 * Reads up to <code>len</code> bytes of data from this input stream
	 * into an array of bytes. If <code>len</code> is not zero, the method
	 * blocks until some input is available; otherwise, no
	 * bytes are read and <code>0</code> is returned.
	 * <p>
	 * This method simply performs <code>in.read(b, off, len)</code>
	 * and returns the result.
	 *
	 * @param b   the buffer into which the data is read.
	 * @param off The start offset in the destination array
	 *            <code>b</code>.
	 * @param len the maximum number of bytes read.
	 * @return the total number of bytes read into the buffer, or
	 * <code>-1</code> if there is no more data because the end of
	 * the stream has been reached.
	 * @throws NullPointerException      If <code>b</code> is <code>null</code>.
	 * @throws IndexOutOfBoundsException If <code>off</code> is negative,
	 *                                   <code>len</code> is negative, or <code>len</code> is greater than
	 *                                   <code>b.length - off</code>
	 * @throws IOException               if an I/O error occurs.
	 * @see java.io.FilterInputStream#in
	 */
	@Override
	public int read(byte[] b, int off, int len) throws IOException {
		int res = super.read(b, off, len);
		if (res > 0) {
			count += res;
			checkLimit();
		}
		return res;
	}

	/**
	 * Returns, whether this stream is already closed.
	 *
	 * @return True, if the stream is closed, otherwise false.
	 * @throws IOException An I/O error occurred.
	 */
	@Override
	public boolean isClosed() throws IOException {
		return closed;
	}

	/**
	 * Closes this input stream and releases any system resources
	 * associated with the stream.
	 * This
	 * method simply performs <code>in.close()</code>.
	 *
	 * @throws IOException if an I/O error occurs.
	 * @see java.io.FilterInputStream#in
	 */
	@Override
	public void close() throws IOException {
		closed = true;
		super.close();
	}

}
